An advantage of a replacement metal gate (or RMG) process is that the gate stack is protected from potentially damaging conditions, since it is placed at the end of the process. For instance, with RMG a sacrificial or dummy gate serves as a placeholder, e.g., to place the source and drain regions, etc. With conventional RMG process flows, a dielectric is then deposited around the dummy gate which permits the dummy gate to be replaced with a (replacement) metal gate stack. Source and drain contacts may then be formed between the metal gate stacks.
However, with scaled device technology, feature sizes are involved that are smaller than what can be reasonably achieved using direct patterning technology. For instance, gate-to-gate spacing is becoming so small that placing contacts in between the metal gate stacks is extremely challenging. Shrinking the size of the contacts is not always a viable option since that results in an increase in contact resistance.
Therefore, scalable process technology for forming self-aligned contacts would be desirable.